A driving device is a device which can perform the transmission and/or conversion of energy, such as a motor. Because of the reversibility between a generator and an electric motor, the “motor” mentioned herein may include both the electric motor and the generator, or may also be a reversible motor with dual functions. A wide variety of types of driving devices exist, but generally each of them has a stator and a mover. In the present disclosure, a moving part in the device is referred to as a mover, and a relatively fixed part is referred to as a stator. In some driving devices, the mover and the stator are connected by a deformable connection member, a simple example of which is the linear voice coil motor (VCM) which is widely used in the optical field, such as in an auto focus module of a camera of a cell phone.
The basic structure of a voice coil motor is shown in FIG. 1, which generally includes a stator 11, a mover 12 and a spring 13 acting as the deformable connection member. The spring connects the mover and the stator. A load (not shown) is fixedly mounted at the mover. In FIG. 1, the stator is a permanent magnet and a driving coil 121 is wound on the mover. After the driving coil is supplied with power, the mover is linearly moved under the action of the magnetic field of the stator. A movement of the mover in an opposite direction may be achieved by supplying a reverse current to the driving coil or utilizing the restoring force of the spring. In other examples, it is also possible that the mover is a permanent magnet and the driving coil is a part of the stator.
The voice coil motor with the structure described above may precisely position the location of the load (for example, move a focus lens to a desired position) by the balance between the electromagnetic force generated by the driving coil and the elastic force of the spring. In general, the elastic force of the spring is proportional to the displacement thereof in a working range, which leads to that the larger the displacement of the mover, the larger the electromagnetic force required, and the larger the current of the driving coil. When the mover needs to be kept at a fixed position (for example, a position for focusing) for a long time, the current of the driving coil needs to be maintained for a long time, which leads to a larger static holding power consumption of the voice coil motor. For the above reasons, the voice coil motor is generally suitable for a short travel application, such as focusing. However, for a long travel application (such as zooming), it is difficult to be achieved by the voice coil motor due to the excessive power consumption.